Pile hammer cushion block

ABSTRACT

A block of cushioning material arranged to be disposed in a cavity within a drive cap of a pile hammer, the drive cap being positioned on the upper end of a pile for impact engagement by the ram with the block of cushioning material during a pile driving operation, the block of cushioning material being of high heat conductivity and arranged in heat transfer relationship with the inner wall of the cavity whereby hysteresis heat generated within the block of cushioning material during impact driving is conducted by the block to the drive cap acting as a heat sink for ultimate radiation of the heat into the ambient air.

BACKGROUND OF THE INVENTION

In the use of a pile hammer for driving a pile into strata, such as theground, the common practice is to utilize a cushion block, commonlyreferred to as an impact block or dolly, which is disposed within adrive cap referred to also as an anvil or follower, which is positionedon the upper end of the pile for receiving the impact force of the pilehammer ram during the pile driving operation. This cushion block servesthree closely related purposes. First, it reduces metal fatigue bypreventing the ram point from striking the drive cap directly. Secondly,it attenuates the driving force of the ram by absorbing a portion of theenergy passing through it to the drive cap and pile. Thirdly, itattenuates the rebound force from the pile to the hammer. This reboundforce approximates the hammer impact force when the pile approachesrefusal driving. In some cases, the reflected shock wave from the strataagrees in frequency with the rebound of the pile to cause a totalrebound of approximately twice the input force. These events vary over aperiod of time from about 0.003 seconds to 0.017 seconds, depending onthe type of hammer, the pile material and the soil strata.

As the driving force builds up and the time duration shortens, there isan increase in the rate of energy per second passing through the cushionblock. This causes greater deformation and therefore the generation ofmore internal heat referred to generally as hysteresis heat. Suchhysteresis heat is generally defined as the heat generated by thefriction between the molecules of a material or gas rubbing on oneanother when they are compressed or impacted. Such hysteresis heat isdeveloped when compressing air or hammering on metal.

Cushion blocks in use today employ such material as hard wood, micarta,solid nylon discs and the like. These materials all have heat insulatingqualities which prevent the heat from being readily dissipated to themetal drive cap for ultimate removal into the ambient air. Therefore,the temperature of the cushion block rises during the pile drivingoperation and destruction results to the block either by plastic flow orignition.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, a primary object of this invention is to provide a new andnovel cushion block for a pile hammer which rapidly dissipates heatdeveloped during the pile driving operation into the ambient air.

Another object of this invention is to provide a new and novel pilehammer cushion block which utilizes readily available inexpensivematerials such as paper and aluminum foil, paper with foil backing, woodcellular products with foil, impregnated paper and foil, vulcanizedfiber and foil, plastic and foil, cloth and foil, aluminum chips andsynthetic resinous material and a metal together with an elastomericmaterial which have a useful life far exceeding cushion blocks in usetoday.

Still another object of this invention is to provide a new and novelpile hammer cushion block which may be used with a drive cap ofconventional construction, which permits the pile driving operation tobe carried out quickly and efficiently and which virtually eliminatesany damage to the pile during the driving operation.

A still further object of this invention is to provide a new and novelcushion block for a pile hammer which may be formed in a variety offorms, utilizing inexpensive materials, all of which permit rapiddissipation of the heat developed during a pile driving operation andwhich enables the maximum force to be utilized during the impact of theram with the pile during the pile driving operation.

A still further object of this invention is to provide a new and novelmethod for positioning a cushion block for a pile hammer in the blockretaining portion of the pile hammer apparatus which permits the cushionto be easily reduced in diameter insuring a necessary snug fitprolonging the useful life of the block.

The objects stated above and related objects are accomplished in theinvention by the provision of a drive cap having a metal body arrangedto be positioned on the upper end of a pile to be driven, the drive caphaving an upper portion provided with a cavity in the open end of whichthe ram is accommodated during impact driving of the pile. Disposedwithin this cavity is a block of cushioning material of high heatconductivity in heat transfer relationship with the drive cap togetherwith a stike plate disposed in the cavity in overlying relationship withthe surface of the cushioning material so that the hysteresis heatgenerated within the block of cushioning material during impactengagement by the ram of the hammer is conducted by the block ofcushioning material to the drive cap acting as a heat sink for ultimateradiation of the heat into the ambient air.

The invention will be better understood as well as further objects andadvantages thereof become more apparent from the ensuing detaileddescription of a number of preferred embodiments taken in conjunctionwith the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a portion of a pile hammer in anoperative position which incorporates one embodiment of the cushionblock of the invention;

FIG. 2 is a sectional view taken substantially along line 2--2 of FIG. 1in the direction of the arrows;

FIG. 3 is a perspective view of a cushion block utilized in theembodiment of FIG. 1;

FIG. 4 is a transverse sectional view of a modification of the cushionblock of FIG. 1;

FIG. 5 is a view similar to FIG. 1 showing a second embodiment of thecushion block of the invention;

FIG. 6 is a sectional view taken substantially along line 6--6 of FIG.5;

FIG. 7 is a perspective view of a component part of the cushion blockarrangement of FIG. 5;

FIG. 8 is a sectional view similar to FIG. 1 showing another embodimentof the cushion block of the invention

FIG. 9 is a plan view of still another embodiment of the cushion blockof the invention;

FIG. 10 is a sectional view showing the cushion block of FIG. 9 in aninitial stage of manufacture; and

FIG. 11 is a view similar to FIG. 10 showing the cushion block of FIG. 9in the final stage of manufacture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and to FIG. 1 in particular, there isshown one embodiment of the cushion block of the invention designatedgenerally by the numeral 10 in an operative position within an assemblyof parts incorporated in a pile hammer of conventional construction. Asis well known, such a pile hammer includes a drive cap 11 in the form ofa massive steel body which is arranged to be positioned on the upper endof a pile 12 to be driven into strata such as the ground. The drive cap111 may be provided with fins 11a for dissipating heat developed thereininto the ambient air.

The drive cap 11 is provided with a lower cavity 13 having an open end13a for accommodating the upper end or head 12a of the pile 12 to bedriven. The upper portion of the drive cap 11 is provided with a cavity16 having an open upper end 16a for accommodating the point of a ram 17guidably disposed within a hammer base 18.

As specifically illustrative of the invention, the cushion block 10 isdisposed within the upper cavity 16 and has an upper surface 10a onwhich a strike plate 19, circular in cross-section, is positioned forengagement by the ram point 17 during the pile driving operation. Thecushion block 10 is preferably of circular cross-section, having adiameter for nesting snugly within the cavity 16 in heat transferrelationship with the inner wall of the cavity 16 and includes amaterial of high heat conductivity. The heat generated during the piledriving operation is localized within the block 10 in a zone referred toas a hysteresis heat zone H.

In the embodiment of FIG. 1, the cushion block 10 comprises aconvolutely wound cylindrical body as shown best in FIG. 3 wound fromsheet material 21 comprising a multi-ply laminate of metal 22 and paper23. In the preferred embodiment, the metal ply 22 is of aluminum foiland is laminated together in any well known manner with the paper ply 23to form the strip 21 of sheet material. Also, the convolutely wound body10 is preferably provided with a core 24, preferably of wood, on whichthe strip 21 is wound and the body 10 is disposed within the cavity 16with its longitudinal axis extending in the direction of the axis of theram 17 as shown in FIG. 1. In accordance with the invention, a metal ply22 may be provided on both sides of the paper ply 23. Other possiblecombinations of materials for the strip 21 may be a cloth and foillaminate, a laminate of impregnated paper and foil or a laminate of acellulosic cellular material and foil.

It should be understood that portions of the metal component of thecushion block 10 is necessarily in intimate contact with the inner wallof the cavity 16. In order to have heat transfer to the inner walls 16,the multi-ply laminate of metal 22 must be on the outside of the paperply 23 in contact with the inner wall. Therefore, to accomplish this,the aluminum foil ply 22 extends vertically within the cavity 16 withits lower edges in heat transfer engagement with the bottom wall of thecavity. Since the aluminum foil extends vertically in the cavity and isin contact with the bottom of the cavity heat is conducted to the cap11.

In the embodiment of FIG. 4, the strip 21' is formed similarly to thestrip 21 of FIGS. 1-3, and includes a core 26 also preferably of wood,but of cruciform shape as shown around which the strip 21' is wound. Itshould be understood that the cushion block 10 should be snuggly fittedwithin the cavity 16 thereby resisting deformation of the block duringuse.

During the pile driving operation, the heat developed in the cushionblock 10 confined generally to the hysteresis heat zone H is quicklyconducted by the aluminum foil 22 to the inner wall of the cavity 16 inthe direction of the arrows C into the metal body of the drive cap 11 sothat the drive cap 11 acts as a heat sink substantially reducing thetemperature of the cushion block 10. Since the drive cap 11 is exposedto ambient air, the heat conducted into the body of the drive cap isradiated quickly into the ambient air so that the temperature of theblock 10 is maintained at a relatively low level preventing thedeleterious effects of heat on the block 10 which would otherwise occur.

As the diameter of the cavity 16 in various drive caps used in pilehammer apparatus varies, to provide a block 10 in accordance with theembodiment of FIGS. 1-4 having a specific diameter would not necessarilyprovide the required snug fit between the block 10 and cavity 16. It istherefore within the scope of the invention to provide a wound block 10in a diameter somewhat larger than the inner diameter of such cavities16. The leading portion of the multi-ply laminate 22, 23 can then bepeeled away and severed until the resulting diameter of the block 10 issuch as to snugly fit within the cavity 16.

Referring now to FIG. 5, there is shown another embodiment of theinvention wherein like numerals are used to identify like parts. In theembodiment of FIG. 5, the cushion block designated generally by thenumeral 30 is disposed within the upper cavity 16 of the drive cap 11and includes a plurality of rod members 31 pf synthetic resinousmaterial such as a plastic, arranged in parallel relationship within amatrix 32 comprising metal particles such as aluminum chips. The rodmembers 31 are stacked together as shown with their longitudinal axesextending in the direction of the axis of the ram 7 and a particleretaining cover member 33 having an annular flange 34 is disposed overthe upper surface of the matrix 32 in underlying relationship with thestrike plate 19. The annular flange 34 of the cover member 33 ispreferably provided with circumferentially spaced serrations 34a whichaid in retaining the metal particles of the matrix 32 within the cavity16. The circular shape of the cover member 33 is such as to position theflange 34 in snug-fitting engagement with the inner wall of the cavity16. As in the embodiment of FIG. 1, the heat developed in the hysteresisheat zone H within the block 30 is conducted quickly through thealuminum particles forming the matrix 32 to the inner wall of the drivecavity 16 into the body of the drive cap 11 which acts as a heat sinkfor ultimate dissipation of heat into the ambient air.

In the embodiment of FIG. 8, wherein like numerals are used to identifylike parts, the cushion block 40 is formed of a mixture of particles ofsynthetic resinous material such as plastic pellets and particles ofmetal of a high heat conductivity such as aluminum chips. As in theembodiment of FIG. 5, the mixture of particles formed in the block 40are confined in the cavity 16 by means of the cover member 33 and as aresult of the high heat conductivity of the aluminum chips, hysteresisheat is conducted in the direction of the arrows C into the body of thedrive cap 11 for ultimate dissipation into the ambient air.

In the embodiment of FIGS. 9-11, the block 50 is of multi-plyconstruction including a ply 51 of a metal having a high heatconductivity such as aluminum and a ply 52 of an elastomeric materialsuch as a plastic or the like wound convolutely or cast in convoluteform with the ply 51, 52 in alternating relationship as shown in FIGS.9-11. The metal ply 51 has a width greater than that of the elastomericply 52 so, in the initial stage of manufacture, the metal ply 51 hasside edge portions 51a, 51b, extending outwardly on opposite sides ofthe elastomeric strip 52 as shown in FIG. 10. Subsequently, the edgeportions 51a, 51b are folded over into overlying relationship with theside edges of the elastomeric strip 52 to form the configuration shownin FIG. 11. Thus, the edge folded metal ply 51 forms a good conductingsurface for engagement with the inner wall of the cavity 16 and alsoserves to hold any elastomeric fragments in place when work hardeningcracks develop.

As in the previous embodiments, hysteresis heat is conducted from theblock 50 by the metal ply 51 into the drive cap 11 for ultimatedissipation into the ambient air.

Preferably, a cushion block B is positioned within the lower cavity 13of the drive plate 11 and the block B may be constructed similar to anyof the embodiments discussed above relative to the cushion block in theupper cavity 16 of the drive cap 11. Similarly, hysteresis heatdeveloped within the cushion block B is conducted into the body of thedrive cap 11 in the direction of the arrows C for ultimate dissipationinto the ambient air.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. A cushion block for the drive cap of a pile hammerhaving a ram for impact driving a pile into strata comprising, incombination, a drive cap having a metal body arranged to be positionedon the upper end of a pile, said drive cap metal body having an upperportion provided with an upper cavity having an open upper end foraccommodating said ram during impact driving of said pile, a convolutelywound body of cushioning material comprising a multiple laminateincluding a ply of heat conductivity material and a supporting layer ofnon-metallic material so that the longitudinal axis of said convolutelywound body is coaxial with the longitudinal axis of said cavity andcontained and nesting snugly within said cavity in heat transferrelationship with said drive cap and a strike plate disposed in saidcavity overlying relationship with the surface of said block ofcushioning material for impact engagement by said ram whereby hysteresisheat generated within said block of cushioning material during saidimpact driving is conducted by said block of cushioning material to saiddrive cap acting as a heat sink for ultimate radiation of the heat intothe ambient air.
 2. A cushion block as claimed in claim 1 whereinsaidheat conductivity material is metal foil; and said non-metallic materialis a ply of paper material.
 3. A cushion block in accordance with claim2 wherein said metal foil is aluminum.
 4. A cushion block in accordancewith claim 3 wherein said convolutely wound body includes a central coremember of wood on which said multi-ply laminate is convolutely wound. 5.A cushion block in accordance with claim 1 wherein said block ofcushioning material includes a convolutely wound body having a pluralityof plies, said plurality of plies including a strip of metal having ahigh heat conductivity and a strip of synthetic resinous material withsaid strips arranged in alternating relationship, said metal striphaving a width greater than that of the width of said strip of syntheticresinous material and having side edge portions folded over intooverlying relationship with the side edges of said strip of syntheticresinous material.
 6. A cushion block in accordance with claim 5 whereinsaid metal strip is aluminum.
 7. A cushion block in accordance withclaim 1 wherein said drive cap has a lower portion provided with a lowercavity with an open lower end for accommodating the upper end of saidpile and a block of cushioning material of high heat conductivitycontained within said lower cavity whereby the hysteresis heat generatedwithin said cushioning material in said lower cavity during said impactdriving is conducted to said drive cap acting as a heat sink forultimate radiation of the heat into the ambient air.
 8. A method ofsizing a cushion block in a pile hammer apparatus comprising the stepsof:snugly fitting a cushion block of a convolutely wound body of a sheetmaterial within a cavity of a drive cap, wherein said convolutely woundbody of sheet material comprises a multi-ply laminate including a ply ofmetal foil and a ply of paper material, said convolutely wound bodyhaving a diameter slightly greater than the diameter of said drive capcavity, determining the diameter of said drive cap cavity, peeling awaya leading portion of said sheet material to the extent to provide adiameter on said body sufficient for producing said snug fittingrelationship between said cavity and said cushion block body disposedtherein, severing said leading portion from said body, and insertingsaid cushion block in said cavity so that the longitudinal axis of saidconvolutely wound body is coaxial with the longitudinal axis of saidcavity.
 9. A cushion block for a drive cap of a pile hammer having a ramfor impact driving a pile into strata comprising at least one sheet ofheat conductive metalic material and a sheet of non-heat conductivenon-metallic material convolutely wound in a cylindrical body about alongitudinal axis, said convolutely wound cylindrical body positionedcoaxially in a drive cap metal body having at least one longitudinallyextending cavity having an open upper end for accommodating a ram duringimpact driving of a pile with said sheet of heat conductive metallicmaterial in heat transfer relationship with said drive cap metal bodyand a strike plate disposed in said open upper end between said cushionclock and said ram whereby hysteresis heat generated within said cushionblock during impact driving will be conducted by said block ofcushioning material to said drive cap acting as a heat sink for ultimateradiation of generated heat into surrounding ambient air.
 10. A cushionblock as claimed in claim 9, in which said sheet of non-heat conductingnon-metallic material is sandwiched between two layers of metallicmaterial.
 11. A cushion block as claimed in claim 10, wherein saidmetallic layer is aluminum.
 12. A cushion block as claimed in claim 9,wherein said metallic layer is aluminum foil.
 13. A method of using aconvolutely wound composite cylindrical body including an elongatedstrip of heat conductive material adhered to an elongated strip ofnon-heat conductive material comprisingplacing said convolutely woundstructure in a cap cavity of a pile driver with said heat conductivitymaterial in heat conductive relationship with said cap and with itslongitudinal axis coaxial with said cap cavity.